It was found with early explosively-operated tools not having a gas release that the cartridge in the firing chamber was difficult to remove due to the gas pressure from the detonation. This problem was remedied by the inclusion of a piercer pin and passages in the breech cap so that the pin pierces the cartridge upon closing the chamber, and after firing, as the breech cap is backed off slightly, the gases escape through the hole in the cartridge and out through the passages in the breech cap. U.S. Pat. No. 3,292,363, incorporated herein by reference, discloses the piercer pin and passages. Although the disclosed piercer pin and passages solved the problems, it subsequently was found that the pin would wear and not penetrate the cartridge so that the gases could not escape.
It is now proposed to provide a piercer pin which incorporates a way to determine its wear prior to its becoming ineffective.